1. Field of the Invention
The present invention relates to a dishwasher and more particularly, to a system for supplying heat energy for heating wash liquid in a dishwasher in response to the soil load in the dishwasher.
2. Description of Related Art
Domestic dishwashers in use today draw wash liquid from a sump at the bottom of a wash tub and spray the wash liquid within the wash tub to remove soils from dishes located on racks in the tub. It is well known that the removal of soils from the recirculating wash liquid positively impacts the wash performance of the dishwasher. Accordingly, to improve performance and efficiency, some dishwashers employ a system for separating soil out of the recirculating wash liquid wherein the soils are retained in a collection chamber.
Wash performance in a dishwasher is also related to the temperature of the dishwashing liquid. It is known that hot water is more effective for washing than cold water, particularly for oily soils which melt at higher wash liquid temperatures. Accordingly, dishwashers are commonly connected to a hot water supply such that the fill water supplied into the dishwasher has a relatively high temperature. To further improve performance, some dishwashers allow users to select a heavy wash cycle (sometimes referred to as a Pots & Pans cycle) which provides for the addition of heat energy to raise the temperature of wash liquid during portions of the wash cycle. Such thermal inputs during the dishwasher cycle typically occur during a thermal hold wherein the cycle of operation is interrupted while a heater is energized until a thermostat is satisfied or a maximum default time limit elapses.
Unfortunately, the addition of heat energy to raise the temperature of the wash liquid in a dishwasher only occurs when the user selects a heavy wash cycle, and once selected, thermal energy is added to the wash liquid regardless of actual soil load on the dishes. Accordingly, in some circumstances, heavily soiled dishes do not receive any additional thermal energy input because the operator fails to select a heavy wash cycle. This results in poor wash performance. In other circumstances, dishes which are relatively lightly soiled and do not require additional thermal input are subject to a wash cycle including additional heat energy inputs because the dishwasher operator erroneously selected a heavy wash cycle. This results in unnecessary energy usage.
Accordingly, it would be an improvement in the art if a dishwasher wash system was provided which automatically added heat energy into a dishwasher in response to the soil level of the dishes.